The present invention relates to the fabrication of semiconductor devices. More particularly, the present invention relates to disposable spacers, methods of forming such disposable spacers, and methods of using such disposable spacers.
As the size of semiconductor devices decreases, various problems arise. Particularly, the control of device characteristics, such as transistors, becomes more difficult as the feature size of devices goes below one micron. In order to control device characteristics, it is important to control processes such as ion implantation and etching during the fabrication of these devices. One technique for controlling such processes involves the use of permanent spacers and disposable spacers. For example, spacers may be utilized to offset the implantation of ions relative to another structural feature of the device or offset an etch of a material relative to a different region of the device being fabricated.
For illustration, in submicron CMOS technologies, PMOS devices typically show a short channel behavior, which is partly caused by lateral diffusion of a dopant, such as boron, into the gate channel of the PMOS device after implant of active areas of the PMOS device. Although, typically, a permanent spacer is utilized for offset of the ion implant from the gate edge in order to widen the gate channel, the spacer width for the PMOS device is usually determined based on the spacer width necessary to create an adequately sized gate channel for NMOS devices fabricated at the same time. Such a spacer width is typically too small to account for the larger diffusion of, for example, boron, into the gate channel of the PMOS device, as opposed to the diffusion of arsenic into the gate channel of an NMOS device. As such, the gate channel is usually shorter than desired for the PMOS device.
Typically, the gate has a large stack height that permits the formation of an additional spacer for PMOS devices to offset the ion implant (i.e., boron) further from the gate so as to allow for greater lateral diffusion in the underlying substrate. Various spacer materials are available; however, use of such spacers creates other problems. For example, a polysilicon spacer could be utilized to offset the implant. However, the removal of the polysilicon spacer after the implant is performed, is difficult to achieve without leaving stringers or over etching into the poly gate or substrate. Further, for example, a silicon nitride spacer if used creates too small of a permanent gap between narrowly spaced gates (i.e., wordlines) for the formation of a bit line contact therebetween. Further, for example, an oxide spacer could also be utilized. However, the removal of the oxide spacer would lead to a loss of field oxide.
An additional illustration of controlling semiconductor device characteristics through the use of fabrication techniques includes the use of an ion implantation in a local oxidation of silicon (LOCOS) process to optimize isolation between the active areas of the devices fabricated. Such a field implant during the LOCOS process is commonly referred to as a channel stop implant. However, the channel stop implant introduces a dopant diffusion encroachment problem wherein the dopant laterally diffuses into active area/channel regions formed by the LOCOS process. The overall effect is that the width of the channel/electrical active area being formed by the LOCOS process is undesirably reduced.
More particularly, a silicon nitride mask is typically utilized as the oxidation mask for the LOCOS process. Although spacers have been formed relative to the silicon nitride mask for offsetting the channel stop implant, such spacers also cause problems as in the case of polysilicon, silicon nitride, or oxide spacers. Such problems include changing the shape of the field oxide grown, removal of portions of the field oxide during etching of the spacer such as with use of an oxide spacer, or, for example, some of the materials may not be selectively etchable relative to the oxidation mask. For example, if a silicon nitride spacer is utilized with a silicon nitride oxidation mask, selective removal would not be possible.
For the above reasons, there is a need in the art for new disposable spacers, in addition to methods of forming and using such spacers to provide desirable semiconductor device characteristics. The present invention, as described below, overcomes the problems described above and other problems which will become apparent to one skilled in the art from the description below.
The present invention includes a disposable spacer for use in a semiconductor device fabrication process. The disposable spacer is formed of a germanium-silicon alloy.
In one embodiment of the invention, the germanium-silicon alloy includes a first portion (x) of germanium and a second portion (1-x) of silicon, wherein x is greater than about 0.2. In another embodiment of the invention, the germanium-silicon alloy includes a first portion (x) of germanium and a second portion (1-x) of silicon, wherein x is greater than about 0.7.
A method of forming a disposal spacer in accordance with the present invention is also described. The method includes providing a device structure and depositing a layer of germanium-silicon alloy on the device structure. The layer is then etched to form the disposable spacer.
In one embodiment of the forming method, the layer is dry etched to form the disposable spacer. In additional embodiments of the forming method, the device structure includes a substrate and a gate structure with the disposable spacers formed at sidewalls thereof. Further, the gate structure may have permanent spacers formed at sidewalls thereof. The disposable spacers are then formed upon the permanent spacers. Further, the device structure may include a substrate having an oxidation mask formed thereon with the disposable spacers formed relative to sidewalls of the oxidation mask.
In another method in accordance with the present invention for use in fabricating semiconductor devices, the method includes providing a first region of material and a second region of material positioned relative to the first region of material. A disposable spacer is formed using a germanium-silicon alloy adjacent a portion of both the first region of material and second region of material.
In one embodiment of the method, a portion of the first material offset relative to the second region of material by the disposable spacer is materially altered. Further, the material alteration may include implanting the portion of the first region of material offset relative to the second region of material by the disposable spacer. Further, the material alteration may include etching the portion of the first region of material offset relative to the second region of material by the disposable spacer.
In another embodiment of the method, the method includes removing the disposable spacer. Further, the removing of the disposable spacer may be performed by oxidizing the spacer to form volatile GexSiyO. Any unvolatilized GexSiyO may be removed using water. Further, the removal step may include removing the spacer with a cleaning solution including ammonium hydroxide.
In another method in accordance with the present invention for use in fabricating semiconductor devices, the method includes providing a first region of material and forming a second region of material at a position relative to the first region of material. The second region of material has a surface in contact with and extending from the first region of material. A disposable spacer is formed from a germanium-silicon alloy on a portion of the surface of the second region of material. The disposable spacer extends over a first portion of the first region of material. A second portion of the first region of material offset relative to the second region of material by the disposable spacer is then implanted.
In yet another method in accordance with the present invention for use in fabricating semiconductor devices, the method includes providing a first region of material and forming a second region of material at a position relative to the first region of material. A disposable spacer is then formed of germanium-silicon alloy in contact with a portion of the second region of material. A portion of the first region of material offset from the second region of material by the disposable spacer is then etched.
Another method for use in fabrication of semiconductor devices is also described. The method includes providing a device structure and forming a germanium-silicon layer on the device structure. A disposable spacer aligned to a first portion of the device structure is formed from the germanium-silicon layer to allow for materially altering a second portion of the device structure. The second portion of the device structure is offset relative to the first portion of a device structure by the disposable spacer.
A method for use in fabrication of MOS devices is also provided. The method includes providing a substrate and having a gate structure formed thereon. The gate structure includes at least one sidewall. A germanium-silicon layer is formed over the gate structure and substrate. A disposable spacer is formed from the germanium-silicon layer on the at least one sidewall and a portion of substrate offset from the gate structure by the disposable spacer is implanted.
In one embodiment of this method, the substrate includes both PMOS and NMOS devices fabricated thereon. The disposable spacer is used to offset implant of the substrate relative to the gate structure of a PMOS device.
In another method for use in fabrication of semiconductor devices, the method includes providing a substrate having an oxidation mask thereon. The oxidation mask includes at least one sidewall. Oxide is formed on the substrate. A germanium-silicon layer is formed over the oxidation mask and substrate, and a disposable spacer is formed from the germanium-silicon layer on the at least one sidewall. The substrate offset from the oxidation mask by the disposable spacer is implanted.
In various embodiments of the method, the oxidation mask is a silicon nitride mask. Further, the germanium-silicon layer is formed, the disposal spacer is formed, and the substrate implanted before or after the oxide formation. And yet further, the substrate may be implanted at a point during oxide formation.